On the older Tacx systems, there was an option whereby you could race your older times - they would appear as other riders.
Granted, Zwift is different in that it’s a public platform, though if only the user could see their old ‘ghosts’ and try to beat older times, it would add motivation during the ride.
If there was an option to design your own race while riding against your older times, it would also allow riders to appreciate their own gains as training gets more intense.